X-37B space plane at rest

A shroud of darkness becomes the X-37B Orbital Test Vehicle, the unmanned space plane design that twice has ventured into orbit on hush-hush missions for the U.S. Air Force. Oh, the Air Force and X-37B maker Boeing don't mind telling you about the launches and landings and the vehicle's remarkable endurance. Just don't bother asking detailed questions about what they're doing with all that time in orbit.

This photo shows the first X-37B, designated OTV-1, on the runway at Vandenberg Air Force Base in California on December 3, 2010, just after it returned from its first trip into space, which lasted 224 days. As it turns out, that was just a warmup act. Any day now, the second X-37B, OTV-2, will touch down on Earth to end its second mission, which began with a liftoff on March 5, 2011 -- meaning it has now been in orbit for better than 465 days, easily doubling the record of its older sibling.